1. Field of the Invention
The present invention relates to a system and a method for detecting a rotational speed of a turbocharger.
2. Description of the Related Art
Published German patent application document DE 10 2010 003 347 A1 describes a method for determining information about a rotational speed of a compressor, in particular a turbocharger, including the steps of providing a measuring signal, in particular a microwave measuring signal, which is directed at a compressor impeller of the compressor, so that the measuring signal is reflected at rotating blades of the compressor impeller, and detecting the measuring signal reflected by one or multiple blades, and determining the information about the rotational speed of the turbocharger as a function of the reflected measuring signal.
Furthermore, a device for determining information about a rotational speed of a compressor, in particular a turbocharger, is described, the device having a signal source for providing a measuring signal, in particular a microwave measuring signal which is directed at a compressor impeller of the compressor so that the measuring signal is reflected at rotating blades of the compressor impeller, a sensor element for detecting the measuring signal reflected by one or multiple blades, and a control unit for determining the information about the rotational speed as a function of the reflected measuring signal.
FIG. 1A shows a cross-sectional representation through a turbocharger 101 known from published German patent application document DE 10 2010 003 347 A1, perpendicular to an axial direction of a shaft 102 which is rotatably supported in a turbocharger housing. FIG. 1B shows a cross-sectional view along the line S-S of FIG. 1A in the direction of the arrow of a turbocharger 101 known from published German patent application document DE 10 2010 003 347 A1.
Turbocharger 101 has a compressor impeller 103 including blades 104 and which is situated on shaft 102. Air is drawn in via an intake opening 105 in the axial direction of shaft 102 by rotation of compressor impeller 103 in turbocharger 101, compressed by blades 104 of compressor impeller 103, and discharged via an exhaust port 107 which is situated in a spiral configuration around compressor impeller 103. Compressor impeller 103 has a blade web 108 for each of blades 104 which supports a blade 109 which protrudes from blade web 108 in the axial direction and is also curved in the direction of the preferred direction of rotation of compressor impeller 103. A measuring device 110 is fixedly situated in the housing of turbocharger 101 which is suitable for the contact-free detection of the passing of an outer edge of blades 109. The location of the measuring device must be selected in such a way that measuring signals may be transmitted between measuring device 110 and the blade ends or blade tips virtually without interference. Measuring device 110 includes a signal source 111 for emitting a microwave measuring signal in the direction of blades 109. The measuring signal is provided in such a way that it may be reflected by one or multiple positions of the blade ends of blades 109. Furthermore, measuring device 110 includes a sensor element 112 in order to detect the microwave measuring signals reflected by the blade ends of blades 109. Sensor element 112 is correspondingly adapted to the type of the microwave measuring signal emitted by signal source 111. This means that if signal source 111 emits a radar signal as an electromagnetic signal, sensor element 112 corresponds to a radar wave sensor. Measuring device 110 is connected to a control unit 115. Control unit 115 receives a microwave signal representing the reflected microwave measuring signals from sensor element 112 and carries out an evaluation of the reflected microwave signal. Sensor element 112 provides a corresponding electrical variable such as a voltage signal or a current signal as an electrical measuring signal, the amplitude of which corresponds to an intensity of the reflected microwave signal. It may be provided to detect an excess rotational speed of compressor impeller 103 of turbocharger 101 and to store a corresponding item of information about it. If rotational speed n of compressor impeller 103 of turbocharger 101 exceeds a predefined rotational speed threshold value for a maximum rotational speed, this may be recorded, output, or stored in a memory unit 116 for later retrieval in a suitable manner.
Well known and available systems for rotational speed detection for turbochargers based on inductive systems are fixedly installed on the particular turbocharger housing of the vehicle. Rotational speed sensors based on such systems are unsuitable for use in mobile and type-independent garage diagnostic devices, since these rotational speed sensors form a unit together with the turbocharger, i.e., in the case of an inductive sensor, the sensor is closely adapted to the specific turbocharger type, and tapping the signal for signal evaluation is impossible.